1. Field of the Invention
The present invention relates to a chain tensioner that includes a tensioner body that has a cylindrical plunger bore with an open end, a cylindrical plunger that is slidably inserted into the plunger bore, biasing means, accommodated so as to freely expand and contract inside an oil pressure chamber formed between the plunger bore and the plunger, for biasing the plunger in a protruding direction of the plunge, this chain tensioner maintaining appropriate tension of a chain.
2. Description of the Related Art
It has been common practice to use a chain tensioner for maintaining appropriate tension of a chain. For example, a chain guide mechanism has been known, which slidably guides, by means of a guide shoe, a transmission chain such as an endless roller chain passing over respective sprockets of a crankshaft and a cam shaft inside an engine room, and which uses a chain tensioner to press a pivoting chain guide having the guide shoe to maintain appropriate tension.
For example, as shown in FIG. 8, an endless timing chain CH passes over a drive sprocket S1 attached to a crankshaft and a pair of driven sprockets S2 and S3 attached to cam shafts in an engine room. A chain guide mechanism is formed, wherein a pivoting chain guide G1 and a fixed chain guide G2 guide this timing chain CR.
The fixed chain guide G2 is fixed in position in the engine room with two mounting shafts B1 and B2, while the pivoting chain guide G1 is attached such as to be pivotable around the mounting shaft B0 in the plane in which the timing chain CH runs in the engine room.
The chain tensioner 500 presses the pivoting chain guide G1 and thereby maintains the tension of the timing chain CH at an appropriate level as well as reduces its vibration.
The known chain tensioner 500 used in such a chain guide mechanism includes, for example, as shown schematically in FIG. 9, a tensioner body 510 that has a cylindrical plunger bore 511 with an open end, a cylindrical plunger 520 that is inserted into the plunger bore 511 to freely slide against a cylindrical surface portion 513 of the plunger bore 511, and biasing means that biases the plunger 520 in a protruding direction of the plunger from the plunger bore 511.
The biasing means are formed by a coil spring 540 accommodated inside a cylindrical recess 521 in the cylindrical plunger 520 and compressed between the plunger and the bottom 512 of the plunger bore 511.
Oil is supplied from an oil supply hole 514 formed in the plunger bore 511, so that an oil pressure chamber 501 formed between the plunger bore 511 and the plunger 520 is filled with the oil, and that the plunger 520 is biased in the protruding direction of the plunger by the oil. A check valve 550 (schematically shown as a check ball) stops the oil from flowing out from the oil supply hole 514.
As the plunger 520 reciprocates, the oil flows through a small gap between the plunger 520 and the plunger bore 511, and the flow resistance provides the damping effect of slowing down the reciprocal movement of the plunger 520.
In such a chain tensioner, in the event of an excessive tension developed in the timing chain during use, the pressure in the oil pressure chamber will be too high, which could generate noise or vibration, or cause damage on the timing chain.
To prevent such a situation, chain tensioners provided with a relief valve for relieving pressure when the pressure inside the oil pressure chamber reaches or exceeds a predetermined limit have been known (see Japanese Patent Application Laid-open Nos. 2002-327810, 2011-226534, 2002-130401, 2002-235818, and 2006-125430, etc).